In recent years there has been a substantial interest in environmentally safe disposal of the by products produced as a result of industrial activities. Industrial activities, such as the drilling of oil and gas wells, may produce large volumes of material solids such as shale, sand and gravel as a natural by-product of the activity. Other industrial operations may produce sludge containing such solids as rust and scale as a component. These solids increase the difficulty and the expense of environmentally safe disposal of these by-products. Oil and gas well drilling operations also expose to the surface naturally occurring radioactive material known as NORM from the sub-surface geological formations. The presence of NORM proposes additional environmental and disposal problems.
Typical solids disposal methods include encapsulating the solids for landfills, bulk land filling, storage pits or injecting the solids into abandoned or new wells. The disposal is complicated by the volume and size of the solid particles being encountered. Thus, there is a need for techniques aimed at improving and simplifying the methods used to reduce the size and volume of the solids by products to aid in their disposal.
One method of disposal of solids such as drill cuttings from oil and gas well drilling activities has been described and illustrated in U.S. Pat. No. 4,942,929 to Malachosky, et al. The Malachosky patent discloses a method wherein construction grade gravel is separated from the spent drilling fluid for use as a construction material. The solids not reclaimed for construction use are formed into a slurry and conducted by pumps into an injection well for disposal into subterranean formations. This system has serious drawbacks in that it offers no way to mechanically reduce particle size prior to their injection into the injection well and its subterranean formations. Oversized particles may block the formation pore spaces and impede the flow of the solids into these formations. Further, NORM materials may not be suitable for construction use and may be of a size too large for injection disposal.
Another method to reduce the size and dispose of drill cuttings from oil and gas well drilling operations is disclosed in U.S. Pat. Nos. 5,109,933 and 5,129,469 to James E. Jackson. The Jackson patents disclose a method and system wherein the drill cutting solids are removed from the drilling fluid, conveyed to a shearing and grinding system that converts the cuttings into a slurry with the addition of water. The solid particles are reduced in size by means of a centrifugal pump and the viscous slurry is discharged into an injection pump for high pressure injection into an underground formation. The Jackson system, or variations of it, has been used extensively in the oil and gas industry for disposal of drill cuttings and drilling fluids. However, the Jackson system does have serious drawbacks.
One major drawback of Jackson is that it affords no control over the size of the solids particles that are being reduced. Without size controls, there is a tendency for the pore spaces of the underground formations to be clogged by oversized solids particles when they are injected into the disposal well. Another is that the solids reduction is accomplished by mixing the solids with a carrier liquid and then transporting the mixture to a conventional centrifugal pump which serves to reduce the size of the solids particles as they circulate through the centrifugal pump. The Jackson system requires that the pump turn at an accelerated speed over and above its normal operating speed. This circulation and recirculation at accelerated pump speeds can cause great wear and tear on the centrifugal pumps and on the pump motors which ultimately leads to downtime on the system and additional expense due to the need for increased repair, maintenance and replacement of the pumps and motors.
Another method and apparatus for wet grinding particle solids is illustrated in U.S. Pat. No. 3,998,938 to Andrew Szegvari. The Szegvari patent discloses a system having a pump to repeatedly circulate liquid suspended solids though a comminuting chamber. The Szegvari comminuting chamber has grinding elements comprised of arms or bars on a rotating shaft within the chamber and a grinding media, such as balls or pebbles, through which the liquid suspended solids pass. The rate of fluid flow through the comminuting chamber is 50 to 300 chamber volumes per hour. This system requires the repeated circulation of the fluid volume through the comminuting chamber with the means outside pumps to accomplish the grinding. Further, the chamber volume and its grinding capacity is limited by the presence of the required grinding media.
Another wet grinding device is that disclosed in U.S. Pat. No. 4,098,465 to Karl Heinz Meller, et al. Meller, et al describes a chamber to receive the material to be reduced along with a volume of grinding balls. The chamber has a plurality of grinding zones, and an auger type mixer which moves the solids material and the grinding balls along the auger, through the grinding zones to a discharge chute. Grinding of the solids is accomplished by the violent action of the grinding balls on the solids material as the solids material and balls are moved along the chamber. The volume of the device and its grinding capacity is limited by the additional volume of the grinding balls which are required in the material reduction process.
Consequently, a need exist for improvements in techniques to reduce the size of solids produced as by-products of industrial activities. This will facilitate disposal of these solids with a corresponding increase in efficiency and a decrease in cost of disposal.